Japanese knotweed is a prevalent and noxious weed. It ranges from Alaska to California east through most of the upper Midwest, and has heavily infested the northeast region of the United States and areas of the south and southeast. Japanese knotweed is found in natural areas, parks, gravel bars, and along riverbeds and stream banks, rights-of-way, and roadsides. It is also found in riparian areas and upland sites. Japanese knotweed thrives in moist soils, or where roots are able to grow into most soils. Plants often become established after being discarded from cultivated gardens, or as escapes from abandoned home sites. The spread of Japanese knotweed also occurs from mechanical mowing and the unintentional transport of cut rhizome segments into neighboring landscapes.
Japanese knotweed, a member of the buckwheat family (Polygonacaea) is an upright, herbaceous, shrub-like perennial that often grows to heights in excess of ten feet. As with all members of this family, the base of the stem above each joint is surrounded by a membranous sheath. Stems of Japanese knotweed are smooth (bamboo-like), stout, and swollen at the joints where the leaf joins the stem. Although leaf size varies depending upon environment conditions, age, and other factors, they are normally about six inches (152.4 mm) long, and three to four inches (76.2 to 101.6 mm) wide, broadly oval to somewhat triangular, mostly pointed at the tip, and are alternate on the stems. The stems are hollow, but may be water-filled depending upon soil moisture levels and where it is growing. The lower one to two nodes may often be full of water. The small, pale greenish-white flowers occur in attractive, branched sprays in summer and are followed by small winged fruits. When they appear, seeds are triangular, shiny, very small about 1/10 inch (2.54 mm) long. Seed may not be borne under all growing situations, and normally not under conditions found outside the native range of Asia. Plants grow quickly and often form large thickets or patches. The roots are rhizomes that may extend 30 feet (914.4 cm) in length. Buds along the length of rhizomes may develop into new stems depending upon environmental and cultural conditions. Digging around the base of established plants encourages new vegetative buds to develop along the rhizome system.
Japanese knotweed is able to spread by sprouts from rhizomes of established plants and from sprouts arising from stems that have been severed from the mother plant. Roots and stems are able to develop when stem nodes come in contact with soils that support plant establishment.
Known methods of Japanese knotweed control include foliar application. Foliar Applications are those applications made with spray equipment designed to apply small droplets over the entire plant (stems and leaves). These may be made with backpack applicators or hose-end sprayers. Applicators should use care to treat only the target species, and not desirable neighboring vegetation. Foliar applications on new growth from rhizome segments and cane nodes, have been found to be effective on plants within the first 3 to 4 weeks of growth (Less than 4 feet (121.92 cm) in height). On established root wads, the spraying of new growth may take several applications over several years to achieve control. It is not recommenced in riparian areas. Depending upon size of infestation, foliar applications may require re-treatment during the growing season and possible follow-up treatment in successive years.
Another known Japanese knotweed control method is cut stem applications. Cut stem applications are made by cutting the Japanese knotweed stem between the first and second internode, and delivering into the “well” created by cutting the internode in half. Approximately 10–20 mL are delivered into the well using this method. Depending upon the site, several herbicide options exist for this application method. Cut stem applications have proven to be about 95% effective on mature plants. After regrowth to 4 feet (121.92 cm) on remaining stems a cut stem or injection application should remove any regrowth.
Another known method of Japanese knotweed control is stem injection applications. Stem injection applications are those applications made just below the first or second node about the ground. Typically, a Japanese knotweed probe is used to create a small opening on either side of the stem just below the node. This allows water to escape while the syringe metered to inject 5 mL of herbicide treatment, delivers the treatment dose on a downward diagonal through one of the two holes closest to the applicator. The second hole then may allow pressurized water to escape if the node is full of water. Plants will normally take up herbicide within 20 minutes of injections.
The injection process in riparian areas has been the most effective against plant regrowth, as well as selective to the Japanese knotweed and posed no threat to the environment. Observed results of injections into each cane snowed total control with no regrowth occurring following treatment for 22 months. Each cane must be injected. Each cane has its own separate rhizome system. Even though the injection process is initially time consuming, it is more cost effective than several trips to the same site for foliar applications made over the years with minimum results.
The following represents a list of known related art:
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The teachings of each of the above-listed citations (which does not itself incorporate essential material by reference) are herein incorporated by reference. None of the above inventions and patents, taken either singularly or in combination, is seen to describe the instant invention as claimed.